1. Field of the Invention
The present invention relates to a power consumption reduction method in a mobile radio system.
2. Description of the Related Art
Such a power consumption reduction method is described in Chapter 6.6 and 6.6.1 of the Draft European Telecommunication Standard ETS 300 578, Ninth Edition, March 1997 as published by ETSI, xe2x80x9cGSM Digital cellular telecommunications system (Phase 2); Radio subsystem link control (GSM 05.08)xe2x80x9d. Generally, in digital mobile radio systems, such as a GSM system, RF power control is employed to minimize the transmit power required by a mobile or a base station subsystem whilst maintaining the quality of the radio links. By minimizing the transmit power levels, interference to co-channel users is reduced. Moreover, in a mobile it is important to save power because increased battery life increases call times and standby times. For the latter reason, manufacturers of mobiles are continuously striving to reduce power consumption in mobiles. In Chapter 6.6 of said ETSI document, it is prescribed that a mobile, whilst in idle mode, upon completion of cell selection and when starting the cell reselection tasks, shall synchronize to and read the BCCH information for the 6 strongest non-serving carriers as quickly as possible. Such non-serving carriers usually are assigned to neighbour cells, but can also be assigned to the serving cell. For multi band mobiles the strongest non-serving carriers may belong to different frequency bands. Such BCCH information is broadcast via BCCH carriers. In GSM, radio frequency channels are defined, and numbers are allocated to all the radio frequency channels available to the system. Each cell is allocated a subset of these channels, defined as the cell allocation. The BCCH carrier is a special radio frequency channel of the cell allocation which is used to carry synchronization information and said general information, including the organization of the so-called common control channels such as paging channels, random access channels, and access grant channels used for setting up radio links between mobiles and the GSM network. In Chapter 6.6.1, such monitoring of non-serving cell BCCH carriers, whilst the mobile is in idle mode, is described in more detail. In order to minimize-power consumption, mobiles that employ DRX (Discontinuous Reception) (i.e. power down when paging blocks are not due) should monitor the signal strength of non-serving cell BCCH carriers during the frames of the paging block that they are required to listen to. The mobile shall include the BCCH carrier of the current serving cell (i.e the cell the mobile is camped on) in this measurement routine. Received level measurement samples can thus be taken on several non-serving cell BCCH carriers and on the serving carrier during each paging block. So, in the described system, a mobile employing DRX should perform at least 7 power measurements per paging block. Typically, a paging block comprises 4 frames, and usually a mobile can perform 2 mmeasurements on non-serving carriers per frame. In the given example, the mobile can thus only adopt a power down mode after the 4th frame.
It is ad object of the present invention to provide a power consumption reduction method in a mobile radio system whilst a mobile radio station is in idle mode and is performing monitoring of carriers of non-serving cells, in which the power measurements during paging blocks are speeded up.
To this end a power consumption reduction method is provided for use in a mobile radio station in idle mode and included in a digital mobile system including frequency and time division radio resources, which system comprises at least one radio base station and a plurality of mobile radio stations, which method comprises:
a) broadcasting to the mobile radio station of system messages informing the mobile radio station about the structure of control channels which include paging channels,
b) powering up of the mobile radio station at a start of a block of paging channels intended for it, which block extends over more than one time division multiple access frame, and is a part of a multiframe structure including at least two blocks of paging channels which are timely separated for the same mobile radio station,
c) monitoring by the mobile radio station of broadcast channel carriers of its serving cell and a number of broadcast channel carriers of non-serving neighbor cells, by measuring receive field strengths thereof,
d) carrying out of non-uniformly spread field strength measurements during the frames preceding a last frame of the intended paging block, and
e) powering down of the mobile radio station at least one time slot earlier than would have been needed if the measurements were uniformly spread over the intended paging block.
Herewith, it is avoided that power measurements are done in the last frame of the paging block so that the mobile can adopt a power down state within the shortest possible time. Thus, in this phase, optimum power consumption reduction is achieved.
The present invention is based upon the insight that full advantage can be taken of the fact that less severe demands are to be put on synthesizer stabilization when performing carrier monitoring as compared to tasks such as equalization. So, more carrier measurements can be squeezed in one frame. Furthermore, is was realized, that anyhow the last paging block should be read but that it should be avoided to do carrier measurements during the last frame of the paging block.
In an embodiment of the invention, during a given frame before the last frame of the intended paging block more field strength measurements are carried out than in other frames before the last frame. The additional measurement or measurements can thus be spread over frames preceding the last frame of a paging block.